This disclosure is directed to an improved bead form insecticide. It is particularly intended for use with fire ants. A colony of fire ants is protected by the imposition of tasters between the ants which forage in the field and the queen which propagates the life of the colony. Thus, insecticides which require ingestion may very well kill the ants of the colony, but rarely, if ever, reach the queen; the colony may thus be reduced in population, but it will typically not be eradicated.
A desirable form of poison for fire ants is Dursban.RTM. insecticide.
Fire ants typically will not carry exposed insecticidal material into the colony. Rather, it must be in a bait form where the fire ants carry it into the colony and thereafter penetrate it to ingest the carrier and the insecticide. Encapsulation prepares the insecticide for ant removal into the colony. Ideally, the foraging ants pick up the encapsulated active ingrediant and carry it into the colony where the microcapsule is penetrated and the core containing the soybean oil and the active ingredient is ingested.
The encapsulation requirements impose a somewhat delicate balance. The surrounding shell about the core must be sufficiently tough to be mechanically handled from the time of manufacture, bagging, transportion and field dispersion. On the other hand, the shell must be sufficiently soft to enable the insect to penetrate it. Moreover, the shell must be impervious to the poison within; this means the shell must be attractive to the insect and yet not bleed so that the enclosed fumigant poison leaks through. Moreover, the shell must be of sufficient thickness in conjunction with toughness to assure the mechanical handling mentioned above. The balance of factors relating to shell fabrication including size requirements are fully met with the melt extrusion processes for microencapsulation as described below in detail.
This process is to be distinguished from microencapsulation accomplished via interfacial polycondensation procedures typically involving two part polymer systems and a liquid carrier. Such processes typically form a shell having a polyamide-polyurea mixture. Other polymer systems for interfacial polymerization formed shells are known. It is relevant to the present disclosure to note that a shell around the core is ideally impermeable and impervious to the core material being primarily an attractant for the insect species. Moreover, the surrounding shell must be reasonably rugged and durable, typically capable of storage in conventional conditions for months and wherein the shell is able to mechanically protect the stored core within without detrimental deterioration during storage. When dispersed, it may well be required to withstand rugged weather conditions including contact with water for a period of time. It is particularly desirable that the capsule have a size of about 300 to about 700 microns with sufficient insecticide within to enable the targeted fire ants species to pick up such capsules. The process of this disclosure sets forth a procedure where a proper shell can be formed around the core which shell has the requisite mechanical characteristics, is impervious to the core, and is not water soluble, is able to mechanically survive from fabrication through dispersal and yet is able to be broken open by the insect.
The present disclosure contemplates use of fire ant toxicants which when ingested will eradicate an insect colony.
One important feature of the insecticide formed by this process is a core payload in the range of about 60-70%. If desired, the core payload can be slightly increased, but it is believed that the payload range of about 60-70% is particularly desirable. This enables the core to adequately contain sufficient insecticide for fire ant eradication.
Many objects and advantages of the method of manufacture and the product formed thereby will be noted on review of the description of the preferred embodiment set forth here below.